With dual-energy scans executed with such dual-energy CT systems the primary objective is to extract the multi-spectrum information which is contained in the image data from the different x-ray energy spectrums. This requires low-noise input images from the two spectrums, preferably this image data should exhibit a similar noise level.
As regards the CT system itself, dual-energy imaging is primarily limited by the maximum quanta flow in the low-energy spectrum. An increase in the flow in the high-energy spectrum to reduce the overall noise is actually possible, but does not bring any significant gain in the evaluation of the dual-energy CT images and, even with a noise-weighted sum image, leads to a worse contrast-to-noise ratio than would be theoretically possible for evenly-distributed noise.
It is known from the prior art that for processing this CT image data, edge-retaining noise reduction methods can be applied to the image data recorded with different spectrums. In relation to this method the reader is referred to DE 10 2004 008 979 by way of example, the entire contents of which are hereby incorporated herein by reference. The disadvantage of the method described therein is that the entire information contained in the data is not able to be used, but that each spectrum is regarded as a self-contained scan and is dealt with in relation to its noise reduction.